serial: sh-sci: Fix build failure for non-sh architectures.

This patch fixes a build failure for various arm based defconfigs
[1][2][3] and maybe other architectures/configs.

The build failure was introduced by the sh specific patch [4]
"serial: sh-sci: Add DMA support"
by Guennadi Liakhovetski

Patch against linux-next of 20100309

References:
[1] http://kisskb.ellerman.id.au/kisskb/buildresult/2248992/
[2] http://kisskb.ellerman.id.au/kisskb/buildresult/2248996/
[3] http://kisskb.ellerman.id.au/kisskb/buildresult/2248998/
[4] http://git.kernel.org/?p=linux/kernel/git/sfr/linux-next.git;a=commit;h=73a19e4c0301908ce6346715fd08a74308451f5aSigned-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

include/linux/serial_sci.h

@@ -2,7 +2,9 @@
 #define __LINUX_SERIAL_SCI_H
 
 #include <linux/serial_core.h>
+#ifdef CONFIG_SERIAL_SH_SCI_DMA
 #include <asm/dmaengine.h>
+#endif
 
 /*
  * Generic header for SuperH SCI(F) (used by sh/sh64/h8300 and related parts)
@@ -30,8 +32,10 @@ struct plat_sci_port {
 	upf_t		flags;			/* UPF_* flags */
 	char		*clk;			/* clock string */
 	struct device	*dma_dev;
+#ifdef CONFIG_SERIAL_SH_SCI_DMA
 	enum sh_dmae_slave_chan_id dma_slave_tx;
 	enum sh_dmae_slave_chan_id dma_slave_rx;
+#endif
 };
 
 #endif /* __LINUX_SERIAL_SCI_H */